The Motherload

[Maltelec]

Gas pipe generally isn't tested at 200C (390F) as you would get in a boiler.

[Lopez Mike]

True. But the strength v.s. temp curves for steels are pretty flat. Now if we were talking about 7075 aluminum I would REALLY start to worry.

Mike

[fredrosse]

Much of the boiler design/construction/materials issues have previously been addressed, starting on page 3 of the forum thread "From napkins to fabrication VFT boiler design". About 18 months ago, but good input from several of the well experienced steamboaters, trying to educate a young man who needed to learn a few things about boilers.

[barts]

I hope that we can continue to design, weld and use boilers of our own construction in our personal boats. Safety is an on-going and real concern, but for our small boilers and low pressures the risk of catastrophic failure remains very low if they are constructed from pipe ample for the pressures and temperatures involved. To drive towards standards deemed suitable for 24/7 operation at high pressures in large industrial environments seems to me to be somewhat overdoing things.

I don't drill and safety wire all the bolts in my boat, although that's standard practice for both airplanes and auto/motorcycle racing. I don't use ultrasonic or radiographic inspection of my (self-built) boat boiler. The materials I used to construct the boiler were not traceable; I'm sure the welding I did wasn't perfect, although I did follow standard boiler/pipe welding protocols.

I understand that some may not be comfortable with this approach, and this isn't a criticism of anyone's approach to safety in our hobby; it's simply how I feel about it.

- Bart

[steamdon-jr]

I am not 100% set on code boilers because a code boiler will still only be a quality boiler if the welder felt like doing a good job that day, once a stamp is issued they can get lax and try to cut corners as Benson Mountain proved to quite a few of us. I do however believe in a well built boiler and there are quite a few non code boilers being built by reputable manufacturers with the appropriate materials. Think of all the changes in the steam loco world due to the Gettysburg Railroad and also the Medina incident. One failure in our boilers that involves injury or worse death could be detrimental to our hobby....play it safe.

[DetroiTug]

We should never use a welded seam shell for boiler construction - just as the code calls out ASTM A106 seamless. The shell of any boiler is the most important component of structural integrity.

Here is a video report of a boiler failure that happened in Canada. Due to the changes in metal composition around the weld, it was a target for premature deterioration.

This boiler had just been inspected including a hydro test.



-Ron

[stevey_frac]

Presumably ASME code has changed since this boiler was constructed? As they said there was no flaw in design or construction...

[fredrosse]

Actually the ASME Boiler Code does allow welded seam boiler shells, HOWEVER if the shell is not seamless, then the seam must be radiographed, a very expensive process for a one-off builder. The reason for the radiography requirement is to see if there are any flaws in the weld seam, and thus reject the piece if these flaws are found. With a seamless shell, there is no weld to introduce the possibility of a seam weld flaw. For my boiler, the piece of pipe that forms the shell cost about $80 USD in welded pipe, $280 in seamless pipe. The radiograph cost was $1500! So that was a no-brainer to select seamless shell material.

If you are manufacturing many boilers, with shells bigger than our launch boilers, then the seamless shell option can be more expensive than the radiographed weld option. In any event, for our boilers, the seamless steel is always better than the welded, so use of A106 seamless is strongly recommended for boiler shells.

[stevey_frac]

Along a similar vein, what are the rules for welding things TO the boiler? It's on the outside, and it's not pressure bearing directly, but presumably the spot where you weld is now slightly weaker...

[fredrosse]

Along a similar vein, what are the rules for welding things TO the boiler? It's on the outside, and it's not pressure bearing directly, but presumably the spot where you weld is now slightly weaker...

Yes, there are many pages in the boiler code addressing connections to the pressure parts, their strength and their reinforcements, etc. These rules probably occupy more than 100 pages of text, figures, diagrams, etc. within the ASME Boiler and Pressure Vessel Code.

For many of our purposes, simple reinforced and full penetration welded connections are allowed, with standard fittings specifically designed for these applications, such as A-105 "thread-o-lets" and "weld-o-lets". There is a good amount of discussion on another thread within this forum: starting on page 3 of the forum thread "From napkins to fabrication VFT boiler design"